Regions in my scene seem to render with less illumination
Since you have stated you are new to Blender, sometimes deleting objects, lights and other items removes subtle mistakes. Archive your file under a new name, so this operation is very little risk.  The second time you model these objects will be faster than the first.
Delete all the lights and add them back. Logic stated in bullet 1.  
Delete the whole scene and start from scratch.  Logic stated in bullet 1.
I assume you want brightness everywhere.
Add more lights or raise your lights higher along the z axis.  Increase the strength.
Add a more distant larger plane. Orient its face towards your scene. Select the emission shader. See image below.





If desired select Cycles Ray Visiblity Camera to FALSE unchecked. This will prevent the render from showing a bright rectangle.  See image below.





Verify you are satisfied with the render results.